General cellular systems employ single-hop communication that is directly performed between a base station and a radio terminal (e.g. mobile terminal). Besides single-hop communication, multi-hop communication causing a radio terminal to relay traffic from another radio terminal has also been studied (as described in Japanese Laid-open Patent Publication No. 2004-248210).
In the field of mobile radio communications, error compensation techniques for compensating for an error taking place over a radio communication path are used (as described in Japanese Laid-open Patent Publication No. 2006-066948, for example). The error compensation techniques include automatic repeat request (ARQ). In ARQ, a receiver side detects an error on a per packet basis using an error detection code attached to a transmission packet by a transmitter side. If no error is detected, the receiver side then returns an acknowledgement (ACK) signal to the transmitter side, and requests the transmitter side to transmit a next packet. If an error is detected, the receiver side returns a negative acknowledgement (NACK) signal to the transmitter side and requests the transmitter side to retransmit the packet.
To reduce the number of retransmissions of ARQ, hybrid ARQ (HARQ) has been used recently. In HARQ, a reception packet is stored on the receiver side if an error is detected. The reception packet is combined with a packet retransmitted in response to a retransmission request, and a combined packet is demodulated. Reception characteristics during the retransmission are thus improved.
The above-described related art techniques have difficulty in transferring data efficiently. For example, in the multi-hop communication, the relaying by the mobile terminal causes a transfer delay of the data. In the single-hop communication, data is retransmitted from a base station if an error takes place, thus the availability of the base station's radio resources becomes tight.